1. Field of the Invention
The present invention relates to a movable window closure for a glass manufacturing chamber and in particular, for a float glass forming chamber.
2. Discussion of the Technical Problems and Presently Available Techniques
In the float glass manufacturing process, molten glass flows through a forming chamber supported on a bath of molten metal, typically tin. The forming chamber usually has several viewing ports or openings in the chamber wall, which are sealed with glass blocks or windows, for observing the chamber interior. The window edges are sealed to minimize the ingress of the exterior ambient atmosphere into the chamber. More particularly, the atmosphere within the chamber usually has a temperature from about 600.degree. C. (1112.degree. F.) to over about 1000.degree. C. (1830.degree. F.) and includes a reducing gas to prevent or minimize tin oxidation. Tin oxide within the chamber is undesirable because it can condense on the chamber ceiling and can drop onto the molten glass making the subsequently formed glass unacceptable. For this reason, it is necessary to minimize the entry of oxygen into the chamber.
A drawback of sealing the window edges is that deposits on the interior surface of the glass blocks or windows interfere with visibility into the chamber, and therefore require frequent cleaning. Furthermore, when the window edges are sealed, removing the window can result in breakage. To minimize the undesirable deposits on the interior of glass viewing ports, U.S. Pat. No. 3,473,905 to Jago et al. teaches a viewing structure attached to a wall of a glass forming chamber. Facilities maintain a curtain of nitrogen across the interior face of a glass panel fixed in the exterior opening of the viewing structure. Although this structure minimizes the deposits on the interior face of the window, thereby increasing the time interval between cleaning, it does not entirely eliminate them. Therefore, when the glass panel is removed, the problem of breakage still exists.
As can be appreciated, replacing windows by removing the window edge seal is a time consuming process which cannot be easily accomplished without damaging or destroying the windows. Furthermore, problems occasionally arise inside the chamber which require immediate access to the interior of the chamber, and, in the past, windows have been purposely broken to quickly provide the needed access opening. Although this provides the necessary access opening, the time that the chamber remains open until the fractured window is replaced allows excessive oxygen to enter the chamber and is therefore unacceptable.
U.S. Pat. No. 3,762,908 to Labrot et al. teaches a removable closure for sealing an access port in a float glass forming chamber which does not require resealing with refractory mortar each time it is removed. The Labrot closure includes a holding frame for biasing the closure lid against the end of a tubular metal ring. The holding frame includes a pair of hooked members which overhang the top portion of the metal ring and slide into a pair of slotted members attached to the lower portion of the metal ring. The closure lid is attached to the holding frame by a central pin. The holding frame is a generally H-shaped frame having four eccentric levers interspaced along the vertical portions of the H, for biasing the closure lid against the metal ring. Disengagement of the closure lid from the metal ring is accomplished by rotating all four eccentric levers, and lifting the frame upward for disengagement of the hooks from the metal ring and of the lower portion of the vertical frame members from the slot. The entire closure lid and frame are then moved away from the chamber wall, providing access to the chamber through the opening.
Although the teachings of U.S. Pat. No. 3,762,908 eliminates the drawbacks associated with fixably sealed windows, it has other drawbacks. For example, the entire lid and holding frame must be lifted and removed from the wall of the chamber for access to the interior of the chamber. The removal of the entire lid is a time limitation when quick emergency access to the interior of the chamber is desired. Furthermore, if the lid is provided with a glass viewing area, hurried removal of the lid and/or placement near the opening can lead to inadvertent breaking of the glass. Still a further drawback of the Labrot closure is that the holding frame obstructs the view into the chamber when the closure is in place, because the biasing mechanism and the frame are, by design, necessarily located within the perimeter of the opening in the chamber wall.
As can be appreciated, it would be advantageous to have a window closure to provide access to the interior of the chamber which does not have the drawbacks of presently available windows.